Thou shalt truly tithe all the increase of thy seed
This was a different tithe from that which was made and given to the Levites, and out of which a tithe was taken and given to the priests, and which they only ate of; but this, as appears by the following verse, was what the owners themselves ate of, and so the tithing was left to be made by them themselves, and which they were to be sure to make, and to make it truly and faithfully:
that the field bringeth forth year by year;
being ploughed and sowed yearly, the produce of it was to be tithed yearly; the Jewish writers
F20 observe on this, that it must be what the earth produces, and is fit for food: and it must be thy seed, which is especially thine, and is not common, but has an owner, and this excludes mushrooms which thou sowest not, and therefore cannot be called thy seed.
F20 Ib. in Misn. Maaserot, c. 1. sect. 1.